There are two principal purposes of the present research. One goal will be to gather and integrate information on the effects of gonadal steroids on the non-reproductive behaviors of several species of rodents, focusing on the behaviors that affect body weight and composition (e.g., eating, taste preferences, voluntary exercise, thermoregulation, dietary self-selection). A second goal of the program is to study, with biochemical methods, the mechanisms by which steroid hormones affect brain tissues, and thus behavior.